Application of IMEP and MBF50 indexes for controlling combustion in dual-fuel reciprocating engine

Abstract

Engine control must take into account both the torque values and the combustion process. The first of these values can be controlled using the knowledge of IMEP, while the combustion process can be evaluated using the angle at which 50% of heat is released (CoC − Center of Combustion). The inclusion of these two values in the control strategy was the main objective of the study presented in this article. The tests were performed on a single-cylinder test engine. The share of gaseous fuel was set from 0 to 80% (for IMEP = 5 bar) and up to 99% (for IMEP = 9 bar). Tests of the combustion process were performed for three different cases: control with fixed IMEP settings, constant combustion angle CoC, and using both control strategies simultaneously. Utilizing a full engine control strategy allows for increased combustion rates: the maximum cylinder pressure is increased by 23% at low loads and 19% at high loads. The influence of such control on the heat release rate in the range of partial load was shown.As a result of using a two-parameter engine control strategy, it is possible to obtain optimum settings for the diesel oil and natural gas doses at which the Pareto optimum is obtained. It has been found, that at partial engine load maintaining constant IMEP or alternatively a constant CoC is difficult. Operation at heavy load indicates bigger compatibility with strategy to keep both IMEP and CoC constant. Operation in such conditions, with a large share of gas fuel energy, requires a larger dose of diesel oil to keep the values of thermodynamic parameters within the acceptable range, as well as to limit the increase in THC emission.